[rspec-devel] Proposal: when_it syntax

Zach Dennis zach.dennis at gmail.com
Sun Oct 5 11:00:37 EDT 2008

I forgot to ask. Have you been using when_it yourself? What experience
have you had with it?


On Sun, Oct 5, 2008 at 10:54 AM, Zach Dennis <zach.dennis at gmail.com> wrote:
> On Sun, Oct 5, 2008 at 5:23 AM, Antti Tarvainen <antti.tarvainen at iki.fi> wrote:
>> Hello.
>> I propose a new syntax that helps DRY up specs when using
>> one-expectation-per-example style. There have been similar proposals
>> before, but no patches. As far as I know, the idea wasn't killed, just
>> forgotten.
>> The patch adds a new "when_it" method and a new parameter to the "it"
>> method. "When_it" describes the action of the example, allowing "it"
>> parts to describe only the expectation.
>> The new parameter to "it" is called :implicitly, and it means that the
>> expectation should be run before the "when_it" part. (That is, it is a
>> mock expectation, and regards the implicit interface of the object.)
>> "It" parts without the :implicitly parameter are run after the
>> "when_it" part.
>> Here's an example of the syntax:
>> describe Controller do
>>  before(:each) do
>>    @model = mock("model").as_null_object
>>    @view = mock("view").as_null_object
>>    @controller = Controller.new(@model, @view)
>>  end
>>  when_it do
>>    @return_value = @controller.act_on(:some_input)
>>  end
>>  it "should get data from model", :implicitly do
>>    @model.should_receive(:data_for).with(:some_input)
>>  end
>>  it "should return :success" do
>>    @return_value.should == :success
>>  end
>> end
>> For a slightly longer example, see http://tinyurl.com/when-it-example .
>> What do you think? The new syntax makes specs more DRY, but does it
>> improve readability?
> I don't think it does.  Here's why IMO:
> * "when_it do" reads horribly. Just read it outloud, it sounds wrong.
> * The word :implicitly that may get appended is a noise word. It is
> not apparent what it does, and it cannot be inferred. It must be
> learned. It also provides no value (outside of technical detail) to a
> reader of the example that body of the it block will be used before
> making the method call, or after making the method call.
> * Using :implicitly means the body of an it block does one of two
> things. For developers this means that they must  always keep the
> context of how the it block will be run when reading the example, or
> writing new ones.
> * when_it can't be used across the board, and nor should it, because
> it separates the call to execute the behaviour from any important
> pre-conditions and also any post behaviour verification. These things
> should be tightly bound together to make the example clear and
> understandable to readers of the code.
> When I say pre-conditions I'm not just talking about what goes in a
> before block. I'm talking about communicating to the reader so they
> don't have to go scrolling up to a before block (let alone up through
> several before blocks). For instance:
> it "finds the most recent project by year" do
>   Project.should_receive(:project_by_year).with("1999")
>   get :show, :year => "1999"
> end
> it "assigns :project" do
>   Project.stub!(:project_by_year).and_return "project"
>   get :show
>   assigns[:project].should == "project"
> end
> Even if a before block stubbed out Project.project_by_year to return a
> project, in the assigns example, I want to explicitly tell the reader
> of the example what it is being assigned to. It doesn't appear that
> you can do this "assigns" example with when_it.
> --
> Zach Dennis
> http://www.continuousthinking.com
> http://www.mutuallyhuman.com

Zach Dennis

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